1. Field of the Invention
The present invention relates to a testing apparatus. More particularly, the present invention relates to structures of a board, generally called a performance board, a probe card or a socket board for mounting a device under test (“DUT”) and a connection unit for connecting the DUT mounting board and the body of the testing apparatus.
2. Description of the Related Art
FIG. 14 shows a schematic structure of a conventional IC testing apparatus, which is described first hereinafter.
In large, the IC testing apparatus includes a main frame 1, a test head 2 and a DUT interface part 3. The main frame and the test head 2 are connected by a cable 4, and the DUT interface part 3 is mounted on and connected to the test head 2.
In this example, the DUT interface part 3 includes, for example, a substrate 11, a motherboard 10 provided with a plurality (e.g. thousands) of cables 12 (“a motherboard unit”), a DUT mounting board 20 generally called a performance board, and an IC socket 320. The substrate 11 is provided with a connector (not shown) for connecting to the test head 2 on its lower surface.
The lower end of the cable 12 is soldered on or connected via the connector to the substrate 11, and the upper end of the cable 12 is connected to the DUT mounting board 20 via a connector (not shown), etc. In this example, one IC socket 320 is mounted on the DUT mounting board 20. As shown in FIG. 14, there is shown DUT (IC under test) 40 mounted on the IC socket 320. Further, there is also shown a cover 13 which covers the cable 12.
FIG. 15 shows a conventional structure of DUT mounting board 20 according to the above structured IC testing apparatus and a schematic connection relationship between the DUT 40 and a connector 15 (on the upper end of the cable 12) in regard to the DUT mounting board 20, where the IC socket 320 is omitted.
The DUT mounting board 20 has a structure of a multilayer printed circuit board, on the upper surface and the lower surface of which electrode pads 21 and 22 are formed for connecting to the DUT 40 and the connector 15, respectively.
Through holes 23 are formed on the corresponding electrode pads 21 and 22 on the upper and lower surfaces of the board 20. The through holes 23 are connected with internal layer wiring patterns 24. In other words, the conventional DUT mounting board has a structure of a multilayer printed circuit board using through holes 23 for connecting the electrode pads 21 and 22 with the internal layer wiring patterns 24. See, for example, in an article of “Build-Up Multilayer Printed Wiring Board Technology”, Page 7 to 8, written by Kiyoshi Takagi, published by Nikkan-Kogyo Newspaper, Inc., Jun. 20, 2000. Arrows in FIG. 14 show flows of electrical signals.
However, recently, high speed testing is required for the IC testing apparatus, and high speed, e.g. 4 Gbps, signals are used for the high speed testing of the DUT.
As the signal speed becomes faster, design of surroundings of the through holes 23 of the conventional DUT mounting board 20 of the above described structure shown in FIG. 15 affects reflections and band blockings.
In other words, as designated by dashed line in FIG. 15, since a stub part 25 (hereinafter, parts unnecessary for transmission lines are called stub parts) for the through hole 23 is large (or long), capacitance of this stub part 25 becomes a problem of producing waveform distortion and capacitive reflection, which cause deterioration of signal quality (or waveform quality). Therefore, the conventional DUT mounting board 20 has a problem of not coping with high speed signals.
Further, in case of conventional testing of electronic devices like semiconductor devices, there have been used a testing apparatus for generating test signals, a performance board for mounting an electronic device and a connection unit for electrically connecting the testing apparatus with the performance board. The performance board and the connection unit respectively have connectors engaging each other. The connector of the connection unit receives test signals from the testing apparatus and provides them to the electronic device via the connector of the performance board.
The connectors of the connection unit and the performance board are respectively fixed on predetermined locations of the connection unit and the performance board, and electrically connect the testing apparatus with the performance board by engaging corresponding connectors as disclosed, for example in Japanese Patent Application Laid-Open No. 2000-81461. For example, respective connectors are provided on neighborhoods of the outermost circumferences of the connection unit and the performance board.
However, since the connector of the connection unit is fixed, it is difficult to connect the connection unit with the performance board where the location of the connector is different. Thus, it is required to prepare each connection unit which has each connector arrangement corresponding to each performance board of different connector location.
For example, in case a high frequency signal is applied to the electronic device, it is required to arrange the connector of the performance board to be near the electronic device in order to shorten the length of the transmission line from the connector of the performance board to the electronic device. In this case, it is also required to arrange the connector of the connection unit on a location corresponding to the location of the connector of the performance board. But, since the connector of the conventional connection unit is fixed, it is required to prepare a connection unit for high frequency signals.